The radiation emitted after just 50 minutes on a mobile phone increases the activity in brain cells, according to a new government-funded study.

The effects of that brain activity are not known, said the researchers, who called for more study.

Phones that were turned off did not create the same brain activity.

The small study, published in the Journal of American Medical Association, is the first to look specifically at how electromagnetic radiation from cell phones affects glucose metabolism, a normal function, in the brain.